Building barriers has been used for thousands of years to protect things. That age-old practice is also useful in the modern context of protecting the Waikato’s waterways, especially as we collectively move to beef up our guardianship of lakes, rivers, streams and groundwater.

The National Policy Statement for Freshwater Management and related moves to change the regional plan underpin existing moves being made to protect them more from contamination and degradation.

Well-constructed and planted riparian margins beside water bodies form a barrier that can help to keep contaminants out. These margins - strips of land adjacent to the water-bodies – can, for example filter out contaminants such as sediments, bacteria and nutrients from farm run-off, especially those contained in animal dung and urine, as well as  agricultural chemicals.

Algal growth

Pathogens like giardia and cryptosporidium can cause water-borne diseases, which in turn can cause serious health problems, while nitrates and phosphates can also create health disorders both for people and stock, and contribute to algal growth.

Besides cleaner water generally, an important benefit of good riparian management is improved stock health because stock no longer get their drinking water from contaminated streams. There may also be reduced maintenance effort required for water systems that draw from surface water.

Winter weather can place increased strain on the banks of farm waterways, increasing the risk of stream bank erosion threatening paddocks and affecting water quality.

So it’s particularly timely to look at the issues involved in erosion generally and land management practices that can contribute to contamination of waterways.

Eroding banks

Some of our rivers, lakes and streams have eroding banks, silted beds, water weed infestation and reduced water quality, as a result of the way the land is used.

Land management practices – whether related to farming, forestry, roading or horticulture – can cause soil erosion and a build-up of contaminants into watercourses. 

They include stock wading in water, poor cowshed effluent treatment, overgrazing, inappropriate fertiliser application, pugging and poor runoff control on cultivated land, and construction and use of roads and tracks which can all contribute to the contamination of water bodies. All of these practices can be managed to reduce the risk of generating contaminants.

Riparian margins

In addition to reducing the risks at source, good management of the banks of waterways, with an appropriate and well-planted riparian margin, can create that barrier between the farm system and the water body to help to reduce negative effects by stabilising the banks and providing a filter for contaminants washing off the land.

Besides filtering out contaminants, riparian strips can increase farm biodiversity. Careful selection of the mix of species planted within riparian areas makes it possible to beneficially modify what’s happening with light, temperature, nutrient and sediment loads, channel and bank stability, carbon inputs, and habitat for terrestrial species.

Shrubs and trees with extensive root systems, which tolerate moist soil conditions and frequent silt deposits, are ideal for stream bank erosion control. They physically hold the stream banks together and some tree roots also protect the streambed, limiting the scouring effect of running water.

Streamside vegetation provides shade which cools the water, improves dissolved oxygen levels, helps aquatic life and reduces the risk of algal blooms.

Spawning fish

Suitable plant species beside waterways also provide cover for spawning fish, and food and habitat for nesting and juvenile birds. Streamside trees can link areas of native vegetation together, extending habitat for native birds.

Besides such environmental benefits, riparian planting can also help a farm’s economic bottom line.

Well-designed riparian fencing can be used to improve subdivision, help with mustering, and protect animals from drowning or getting stuck in wet areas. The provision of shelter and shade is also recognised as an important aspect of animal production and health.

Improved milk grades are documented where dairy sheds no longer draw water from contaminated streams. On sheep and beef properties, stock are in better health and have faster weight gain when water sources are no longer contaminated.

The regional council’s catchment management officers are available to provide advice on good riparian management.

• Bala Tikkisetty is a sustainable agriculture advisor at Waikato Regional Council. Contact him on 0800 800401 or email bala.tikkisetty@waikatoregion.govt.nz